How many craters are there

Scientists believe the asteroid must be uncommonly dense to have withstood such bombardment. This image mosaic of asteroid Mathilde is constructed from four images acquired by the NEAR spacecraft on June 27, The outer gas planets do not have solid surfaces, but their moons do.

Most of these moons are rocky, icy worlds with a variety of surface features and compositions. Most of them are cratered, such as Europa, one of the Galilean satellites of Jupiter. Europa's surface is thought to consist of a thick layer of ice overlaying a liquid water ocean.

Comet Shoemaker-Levy Impacts with Jupiter Terrestrial planets aren't the only ones that are hit by meteors, comets and asteroids. The planets known as gas giants, such as Jupiter, don't have a solid surface to keep a record of impacts. However, the impact of comet Shoemaker-Levy in left visible holes in the cloudtops of Jupiter. The lake at the bottom of the crater has a depth of meter feet and contains some of the purest water in the world. The lake has no inlets or apparent outlets, so the water accumulates from rain and snow and is only lost through evaporation.

The crater was discovered in , by a US Air Force plane on a meteorological flight. A relatively young crater, the Amguid Crater is the result of a meteor impact about , years ago. It is located in a remote area in southwestern Algeria.

The perfectly circular meteorite impact crater is meter feet in diameter and 30 meter feet deep. The top of the rim is covered by blocks of sandstones that are several meters in diameter. The center of the crater is flat, and is filled by compacted eolian silts. The Wolfe Creek Crater in Australia was formed by a meteorite that crashed into the earth , years ago.

The 50, had a mass of about 50, tons and left a crater of about meters feet in diameter. The crater that was left was probably about meters deep. Over the next , years the wind gradually filled it with sand and today the crater floor is 60 meters feet below the rim, which rises 25 meters above the surrounding flat desert land. Small numbers of iron meteorites have been found in the vicinity of the crater.

The crater was discovered during an aerial survey in although the Aboriginal people have known the crater for thousands of years. Three processes help Earth keep its surface crater free. The first is called erosion.

Earth has weather, water, and plants. These act together to break apart and wear down the ground. Eventually erosion can break a crater down to virtually nothing. Lake Manicouagan, a ring-shaped lake in Quebec, Canada, is all that remains of a crater from a massive impact over million years ago. Though they were made in , these Apollo 14 astronauts' tracks were easily viewed from a NASA spacecraft in orbit around the moon in tracks highlighted in yellow.

Sure, when they're several miles across it's easy, but what about when they're less than an inch across? Is that a crater, a zap pit , or just part of an undulating lunar surface? There is no definitive answer we could find, but the best estimate is in the table below. It is based on crater size and work done to accurately count craters on the Martian surface. Crater Size. The count of just over five thousand craters over 20km in diameter is accurate, but the next two numbers in the tables are estimates based on other sampling data.

If you limit your question to 'How many craters are on the moon over a kilometer wide? That number of craters found on the moon's surface grows exponentially as crater size shrinks. It's conceivable, for example, that the lunar surface, which is bigger than you think , is covered by half a billion craters over 10 meters across!

Craters give an age to the moon because once they are created, they never disappear from the lunar surface, unlike here on Earth. On the moon, there are no plate tectonics, volcanoes, sea, wind or weather to get rid of them over time. That means that if we know how often meteors hit and count how many hits there have been, we can have a decent stab at working out how old the moon is!

Based on counting lunar craters and comparing that number to the average meteor hit rate, we assume the moon to be somewhere between 4. Incidentally, that is million years younger than previously believed!

Ultimately it is the speed and angle of approach of a meteoroid which determines how big a crater it will leave behind, but the scale is impressive.